Various processes and catalysts exist for the homopolymerization or copolymerization of unsaturated monomers, particularly the polymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. Chiral bis-indenyl metallocene catalysts have been used to prepare highly crystalline isotatic polypropylene and copolymers of propylene and other monomers (Resconi, L. Chem. Rev. 2000, 100, 1253). Non-chiral metallocene catalysts have also been prepared which yield atactic polypropylene and copolymers (Resconi, L. in Metallocene Based Polyolefins, Eds. J. Schiers, W. Kaminsky; Wiley; NY, 2000; 467). While, there are chiral catalysts which operate between these extremes, yielding polypropylene with crystallinity less than highly crystalline and more than amorphous, generally these chiral catalysts give low molecular weight polymer. This is also true for copolymers prepared from propylene and other monomers, using such systems.
U.S. Pat. No. 6,051,522 describes bridged chiral metallocenes as catalysts useful for olefin polymerization. WO2002/01745, US 2002/0004575A1, WO2002/083753A1, and U.S. Pat. No. 6,525,157 disclose processes for the preparation of a propylene/ethylene copolymer containing tacticity within the propylene sequences using the chiral metallocene rac-Me2Si(1-indenyl)2HfMe2 and an ionizing activator. U.S. Pat. No. 6,057,408 discloses a process for the preparation of high molecular weight propylene/ethylene copolymers with high crystallinity in the propylene sequences using chiral bis-indenyl metallocenes. The catalyst that yielded the highest molecular weight copolymer was rac-Me2Si(2-Me-4-(1-napthyl)-1-indenyl)2ZrCl2.
S. Collins and coworkers reported (Organometallics 1992, 11, 2115) a study of the effect of substituents in the 5,6-positions on a series of chiral ethylene bridged metallocenes, rac-(CH2CH2)(5,6-X2-1-indenyl)2ZrCl2, on solution ethylene and propylene polymerizations. In comparing X═H and X=Me, similar molecular weights were found for the preparation of polyethylene (X═H, Mn=145 Kg/mol; X=Me, Mn=127 Kg/mol) and polypropylene (X═H, Mn=15.7 Kg/mol; X=Me, Mn=16 Kg/mol). Likewise, In U.S. Pat. No. 5,455,365, chiral bis-indenyl metallocenes containing methyl groups in the 5 and 6 positions and metallocenes containing a phenyl group in the 5 or 6 position are disclosed. Polymerizations at 70° C. in liquid propylene gave moderately crystalline polypropylene, as evidenced by polymer melting points between 132 and 147° C. The molecular weights (Mw) of these materials are between 100 and 200 Kg/mol. Copolymerization of propylene with ethylene, using rac-Me2Si(2,5,6-Me3-1-indenyl)ZrCl2/MAO, yielded a 2.8 wt % ethylene, 97.2 wt % propylene copolymer with a significantly lower molecular weight as evidenced by a drop in intrinsic viscosity from 155 mL/g (Mw=143 Kg/mol) to 98 mL/g (Mw not recorded). This copolymerization also gave a decrease in melting point from 132 to 123° C.
In U.S. Pat. No. 6,084,115, a chiral bis-indenyl metallocene containing an annulated tetramethylated cyclohexyl ring attached at the 5 and 6 positions is disclosed. This metallocene, rac -Me2Si(5,6,7,8-tetrahydro-2,5,5,8,8-pentamethyl-benz[f]indenyl)2Zr(1,4-diphenylbutadiene), is reported to be in the +2 oxidation state. Propylene polymerization behavior was reported in alkane solution (24 wt % propylene) under a partial pressure of hydrogen at 70° C. Molecular weights obtained were ca. 60 Kg/mol and polymer melting points were 144.8-147° C. These molecular weights were lower than the analogous complex with H in the 5 and 6 positions, rac -Me2Si(2-Me-1-indenyl)Zr(1,4-diphenylbutadiene), Mw=79 Kg/mol. Similar results observed in ethylene/octene polymerizations with these two catalysts. No H2-free solution polymerizations were reported. Supported catalysts were also examined in this patent, however broad molecular weight distributions (>3.5) make comparisons between catalysts difficult. These results indicate that a molecular weight advantage is not expected for catalysts with large groups in the 5 and 6 positions. Thus, no meaningful increase in polymer molecular weight can be ascribed to these previous substitutions.
WO 2004/050724 discloses polymerization of butene with methylalumoxane and dimethylsilyl bis[2-methyl-5,6(tetramethyl-cyclotrimethylen)indenyl]zirconium dichloride and also described certain indenyl type compounds with annulated six membered rings; however, WO 2004/050724 does not obtain higher molecular weights at higher temperatures.
Thus there is a need in the art to provide catalyst systems that can provide polymers having high molecular weight as well as good crystallinity preferably prepared at higher temperatures and productivities than otherwise possible.
U.S. Pat. No. 6,479,424 discloses the preparation of unbridged species bis(2-(3,5-di-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl) hafnium dichloride, bis(2-(3,5-di-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)zirconium dichloride, bis(2-(4-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)hafnium dichloride, and bis(2-(4-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)zirconium dichloride which are used to produce propylene polymers.
Other references of interest include: 1) U.S. Pat. No. 6,034,022, (particularly example 17); 2) U.S. Pat. No. 6,268,444, (particularly example 2); 3) U.S. Pat. No. 6,469,188; and 4) EP 1 138 687, (particularly examples 8 and 9).
Further, there is a need in the art to provide processes to produce propylene based polymers having higher molecular weights at higher temperatures, preferably in solution processes. Likewise, there is a need in the art to provide processes to produce propylene based polymers having higher molecular weights at higher temperatures in solution processes using a non-coordinating anion activator, where the propylene concentration in the feed is lower.